1. Field of the Invention
This invention relates to methods and apparatus for applying buffer coatings to optical fibers. More specifically, this invention relates to mold structures utilized in such coating applications.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art
As is known in the art, optical fibers are generally coated with a buffer material to insulate the fiber from the external environment. As the buffer coatings may become damaged by exposure to environmental influences, it is occasionally necessary to reconstitute a portion of the fiber buffer. Reconstitution of the buffer is also required when optical fibers are spliced together--since the buffer in the general vicinity of the splice must be removed. After the fibers have been joined a new buffer coating is applied to the spliced fiber segment. When damage exists solely in the buffer coating and not in the underlying optical fiber, it may suffice to replace a mere portion of the coating.
When a portion of an optical fiber buffer is reconstituted, it is typically important that the original buffer diameter be preserved. For example, small irregularities in the diameter of the coating may preclude the coated fiber from being appropriately wound around a bobbin or other dispensing mechanism. Inappropriate winding of the coated fiber may cause deviation in the desired dimensions of the resultant "fiber pack", thus complicating system design.
The buffer coating surrounding an optical fiber is conventionally reconstituted with use of a "sandwich" type mold. Two rigid Plexiglas plates are inscribed with a semicircular trough. Both troughs are sprayed with teflon to prevent adhesion of the fiber to the Plexiglas. Next, epoxy which will be cured to form the reconstituted coating is placed into the trough and onto the surrounding planar surface of one of the plates. The fiber to be coated is then placed into the trough containing the epoxy and the plates are sandwiched together such that the troughs are in alignment. In this way the fiber and epoxy occupy a cylindrical volume defined by the aligned troughs. The plates are held in place by screws and indexing pins while the epoxy is cured by illumination with ultraviolet light.
Difficulties often arise in connection with the removal of the coated fiber from the Plexiglas mold. For example, despite the presence of the teflon spray the coating epoxy is prone to adhere to the Plexiglas plates. This type of sticking can cause defects in the coating surface. Moreover, the teflon spray may cloud the cured coating. In addition, a thin layer of cured epoxy originating from between the mold plates is typically attached to either side of the reconstituted buffer. This extraneous "mold flash" is partially eliminated by abrasive polishing, but some variation in the diameter of the new buffer coating typically remains.
More fundamentally, the degree to which the diameter of the reconstituted buffer coating agrees with that of the original coating is inherently limited by the accuracy with which the troughs may be inscribed. It is believed that present methods of mechanical inscription yield errors resulting in diameter variations of between 20 and 30 microns.
Accordingly, a need in the art exists for a mold structure capable of accurately reconstituting the buffer coating surrounding an optical fiber.